Gel electrolyte and dye-sensitized solar cell using the same

ABSTRACT

A gel electrolyte including a non-volatile polymer solvent including hydrogen bonding groups with at least two hydrogen bonding sites, and a dye-sensitized solar cell including the gel electrolyte. The dye-sensitized solar cell includes: opposing first and second electrodes; a porous layer disposed between the first and second electrodes, including an adsorbed dye; and the gel electrolyte, which is disposed between the first and second electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/341,199, filed on Dec. 22, 2008, which, in turn, claims priority toand the benefit of Korean Patent Application No. 10-2008-33369, filed onApr. 10, 2008, in the Korean Intellectual Property Office, thedisclosure of each of the above referenced applications is incorporatedherein, by reference.

BACKGROUND OF THE INVENTION

1. Field

Aspects of the present invention relate to a gel electrolyte, and adye-sensitized solar cell using the same.

2. Description of the Related Art

Generally, dye-sensitized solar cells include: a photocathode having asemiconductor oxide nano particle layer, to which dye molecules areadsorbed; a counter electrode including a Pt catalyst; and anelectrolyte including redox ion couples. The electrolyte greatlycontributes to the photoelectric conversion efficiency and durability ofsolar cells. In this regard, liquid electrolytes are commonly used insolar cells.

However, a volatile organic solvent, included in liquid electrolytes,easily volatilizes or leaks, thereby deteriorating the durability ofsolar cells including such liquid electrolytes. Thus, there is a needfor a non-volatile, ionic gel electrolyte, in order to improve thedurability of dye-sensitized solar cells.

Methods of preparing ionic gel electrolytes include: a method of gellinga liquid electrolyte by adding nano particles to the liquid electrolyte;a method of gelling a liquid electrolyte by adding a polymer to theliquid electrolyte; a method of solidifying a liquid solvent by adding agelling agent to the liquid solvent; and a method of polymerizing orcrosslinking monomers, via chemical bonds (US 20030145885A). Among thesemethods, an ionic gel electrolyte, pre pared by adding a polymer to theliquid electrolyte, has far less ion conductivity than the liquidelectrolyte.

According to the method of solidifying the liquid solvent by adding agelling agent, the stability of the solvent may be decreased, as thetemperature is increased. According to the method of polymerizing orcrosslinking monomers via chemical bonds, the temperature should beincreased, and an initiator should be added thereto, in order toinitiate reactions after injecting the monomers into cells. Thus, theefficiency of solar cells may be decreased, and unreacted materials mayreduce the durability of the solar cells. According to the method ofgelling a liquid electrolyte by adding nano particles to the liquidelectrolyte, the gelation properties of the electrolyte are notsatisfactory, even though the ion conductivity is excellent.

SUMMARY

Aspects of the present invention provide a gel electrolyte havingimproved ion conductivity and gelation properties, and a dye-sensitizedsolar cell including the gel electrolyte, which has improvedphotoelectric conversion efficiency.

According to an aspect of the present invention, there is provided a gelelectrolyte comprising a non-volatile polymer solvent having a hydrogenbonding group with at least two hydrogen bonding sites.

According to another aspect of the present invention, there is provideda dye-sensitized solar cell comprising: a first electrode; an opposingsecond electrode; a porous layer, to which a dye is adsorbed, disposedbetween the first electrode and the second electrode; and a gelelectrolyte disposed between the first electrode and the secondelectrode. The gel electrolyte comprises a non-volatile polymer solventhaving a hydrogen bonding group with at least two hydrogen bondingsites.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows, and in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe exemplary embodiments, taken in conjunction with the accompanyingdrawings, of which:

FIG. 1 is a cross-sectional view of a dye-sensitized solar cell,according to an exemplary embodiment of the present invention;

FIG. 2 is a graph illustrating the viscoelastic properties of a gelelectrolyte prepared according to Example 1, as measured by a dynamicmechanical analysis (DMA); and

FIG. 3 is a graph illustrating the photoelectric conversioncharacteristics of a dye-sensitized solar cell prepared according toExample 8.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The exemplary embodiments are described below, in order toexplain the aspects of the present invention, by referring to thefigures.

A gel electrolyte, according to aspects of the present invention,includes a non-volatile polymer solvent having a hydrogen bonding groupwith at least two hydrogen bonding sites. The non-volatile polymersolvent may include a polymer having a hydrogen bonding group, which ishydrogen bonded to a diacid. Alternatively, the non-volatile polymersolvent may include two types of polymers having hydrogen bondinggroups. Thus, the gel electrolyte is an ionic gel electrolyte that canbe solidified by self assembly, without adding a separate crosslinkingagent or gelling agent.

Each of the hydrogen bonding groups may include at least two hydrogenbonding sites, and in particular, from 2 to 4 hydrogen bonding sites.The term “hydrogen bonding group” is used to represent a functionalgroup including atoms with high electronegativities, such as oxygenatoms and nitrogen atoms, which may form hydrogen bonds. The hydrogenbonding group may be any of the compounds represented by the structuresbelow, but is not limited thereto.

As shown above, a functional group capable of forming at least onehydrogen bond is regarded as “a hydrogen bonding group,” regardless ofthe number of moieties capable of forming hydrogen bonds, that is,regardless of the number of hydrogen bonding sites.

The term “non-volatile polymer solvent” refers to a substance which is anon-volatile polymer and functions as a solvent during the formation ofthe gel electrolyte. Thus, an additional solvent, which is used to formconventional gel electrolyte, is not necessary for the formation of thegel electrolyte.

The polymer including the hydrogen bonding group may be a polyalkyleneoxide-based compound, having a hydrogen bonding group at one end, andhaving a weight average molecular weight of 2,000, or less, and inparticular, ranging from 200 to 1,000. If the weight average molecularweight of the non-volatile polymer solvent is greater than 2,000, theion mobility in the gel electrolyte may be decreased, due to anincreased viscosity thereof.

The polyalkylene oxide-based compound may be a polyethylene oxide-basedcompound, a polypropylene-based compound, or the like. The polymerincluding the hydrogen bonding group may be one of the compoundsrepresented by the following Formulae 1 to 3.

In Formula 1, R₁ is a substituted or unsubstituted C1-C20 alkyl group, asubstituted or unsubstituted C6-C20 aryl group, or a substituted orunsubstituted C2-C20 heteroaryl group. R₂ is a substituted orunsubstituted C1-C20 alkyl group, a substituted or unsubstituted C6-C20aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group,and a is an integer from 1 to 50.

In Formula 2, b is an integer from 1 to 50.

In Formula 3, c is an integer from 1 to 50.

The polymer represented by Formula 1 may be a compound represented byFormula 4 below.

In Formula 4, a is an integer from 1 to 33.

The compound of Formula 1 may be prepared by mixing a polyethyleneglycol dimesylate represented by Formula 5 below and calcium carbonate,adding pyrimethamine represented by Formula 6 below to the mixture, andreacting the mixture at a temperature between 60 and 80° C., and inparticular, between 65 and 70° C.

In Formula 5, n is an integer from 1 to 33.

The compound of Formula 2 may be prepared by mixing a polyethyleneglycol-(succinimidyl succinate) represented by Formula 7 below and acytosine represented by Formula 8 below, and reacting the mixture at atemperature between 60 and 80° C., and in particular between 65 and 70°C., in the presence of a solvent.

In Formula 7, n is an integer from 1 to 33.

The compound of Formula 3 may be prepared by mixing a polyethyleneglycol-(succinimidyl succinate) of Formula 7 and a guanine representedby Formula 9 below, and reacting the mixture at a temperature between 30and 45° C., and in particular between 35 and 40° C., in the presence ofa solvent.

In Formula 2, b is generally an integer from 1 to 33. In Formula 3, c isgenerally an integer from 1 to 33.

According to an exemplary embodiment of the present invention, the gelelectrolyte includes a polymer having a hydrogen bonding group and adiacid, which form hydrogen bonds when they are mixed and reacted at apredetermined temperature. The diacid forms hydrogen bonds with thepolymer at hydrogen bonding sites.

Examples of the diacid include glutaric acid, malonic acid, and adipicacid. The amount of the diacid may range from 2.05 to 2.5 moles, permole of the compound of Formula 1. If the amount of the diacid isgreater than 2.5 moles, residual acid may deteriorate gelationproperties of the gel electrolyte and reduce a driving voltage of asolar cell. On the other hand, if the amount of the diacid is less than2.05 moles, unreacted solvent may deteriorate gelation properties of thegel electrolyte.

An example of the non-volatile polymer solvent that is hydrogen bondedto a diacid is shown in the structural formula below. A hydrogen bondinggroup of the polymer represented by Formula 1 forms hydrogen bonds witha hydrogen bonding group of the glutaric acid. Here, each of thehydrogen bonding groups of the compound of Formula 1 has two hydrogenbonding sites.

In the above formula, a is an integer from 1 to 33.

According to another exemplary embodiment of the present invention, thegel electrolyte includes a non-volatile polymer solvent having two typesof polymers having hydrogen bonding groups. Hydrogen bonds are formedbetween the two types of polymers.

As shown in the structural formula below, a hydrogen bonding group A ofthe compound of Formula 2 forms hydrogen bonds with a hydrogen bondinggroup B of the compound of Formula 3. Here, each of the hydrogen bondinggroups A, B have three hydrogen bonding sites.

The amount of the compound of Formula 3 may range from 1.05 to 1.5moles, per mole of the compound of Formula 2. If the amount of thecompound of Formula 3 is not within the range above, unreacted solvent,which does not form hydrogen bonds, may deteriorate the gelationproperties of the gel electrolyte.

The gel electrolyte may include a nano metal oxide, which can enhancethe gelation properties, ion conductivity, and light scatteringproperties of the gel electrolyte. The nano metal oxide may be at leastone selected from the group consisting of TiO₂, WO₃, ZnO, Nb₂O₅, SnO₂,SiO₂, and TiSrO₃. The nano metal oxide may be in the form of nanoparticles or a nano-sized structure. If a particulate nano metal oxideis added to the gel electrolyte, an average particle diameter of thenano metal oxide particles may range from 20 to 400 nm. If the averageparticle diameter is not within the range above, the nano metal oxidemay not adequately improve the conductivity and/or reduce the lightscattering properties of the gel electrolyte.

The gel electrolyte may further include an up-conversion phosphor or adown-conversion phosphor, in addition to the nano metal oxide. Anaverage particle diameter of the phosphors may range from 100 nm to 10μm.

The up-conversion phosphor directly converts ultra violet (UV) lightinto visible light. The down-conversion phosphor directly convertsinfrared (IR) light into visible light, which is absorbed by a dye, toincrease the power generating efficiency of a solar cell.

Examples of the up-conversion phosphor include YF₃:Yb³⁺,Er³⁺,NaYF₄:Yb³⁺,Er³⁺, NaLaF₄:Yb³⁺,Er³⁺, LaF₄:Yb³⁺,Er³⁺, BaY₂F₈:Yb³⁺,Er³⁺, andNa₃YGe₂O₇:Yb³⁺,Er³⁺, but are not limited thereto. Examples of thedown-conversion phosphor include (Sr,Ba,Ca)₂Si₅N₈:Eu²⁺, CaAlSiN₃:Eu²⁺,BaMgAl₁₀O₁₇:Eu²⁺, BaMgAl₁₀O₁₇:Eu²⁺,Mn²⁺, SiAlON:Eu²⁺,(Ca,Sr,Ba)₂P₂O₇:Eu²⁺, (Ca,Sr,Ba)₂P₂O₇:Eu²⁺,Mn²⁺,(Ca,Sr,Ba)₅(PO₄)₃Cl:Eu²⁺, Lu₂SiO₅:Ce³⁺, (Ca,Sr,Ba)₃SiO₅:Eu²⁺,(Ca,Sr,Ba)₂SiO₄:Eu²⁺, (Ca,Sr,Ba)₁₀(PO₄)₆. nB₂O₃:Eu²⁺, Sr₄Al₁₄O₂₅:Eu²⁺,and 3.5MgO.0.5MgF₂.GeO₂:Mn⁴⁺, but are not limited thereto.

The ion conductivity and gelation properties of the gel electrolyte canbe optimized by controlling the number of hydrogen bonding sites of thehydrogen bonding group. The gelation properties, ion conductivity, andlight scattering properties may further be improved, by including thenano metal oxide in the gel electrolyte.

The gel electrolyte, according to aspects of the present invention,includes a non-volatile polymer solvent having a hydrogen bonding groupwith at least two hydrogen bonding sites, as described above. Thehydrogen bonds may be identified by an infrared analysis (IR). The gelelectrolyte may be used as an electrolyte of a secondary battery, acapacitor, or a solar cell.

The gel electrolyte may further include a redox couple. Such anelectrolyte is efficiently used in a dye-sensitized solar cell. Theredox couple may be an iodine (I₂)/iodized salt. I⁻ and I₃ ⁻ ions may beprepared from the iodine and the iodized salt. The I⁻ and I₃ ⁻ ionsreversibly react with each other.

Examples of the iodized salt include lithium iodide, sodium iodide,potassium iodide, magnesium iodide, copper iodide, silicon iodide,manganese iodide, barium iodide, molybdenum iodide, calcium iodide, ironiodide, cesium iodide, zinc iodide, mercury iodide, ammonium iodide,methyl iodide, methylene iodide, ethyl iodide, ethylene iodide,isopropyl iodide, isobutyl iodide, benzyl iodide, benzoyl iodide, allyliodide, imidazolium iodide, and 1-methyl-3-propylimidazolium iodide, butare not limited thereto.

The amount of the iodized salt may be 0.05 to 0.1 moles, per mole of thenon-volatile polymer solvent. If the amount of the iodized salt is lessthan 0.05 moles, the ion conductivity of the gel electrolyte may bedecreased. On the other hand, if the amount of the iodized salt isgreater than 0.1 moles, the viscosity of the gel electrolyte may beincreased, due to mutual interference between the ions.

The amount of iodine may range from 1 to 10 parts by weight, based on100 parts by weight of the iodized salt. If the amount of iodine is lessthan 1 part by weight, the ion conductivity of the gel electrolyte maybe decreased. On the other hand, if the amount of iodine is greater than10 parts by weight, the electron recombination in the gel electrolyte,due to I₃ ⁻ ions, may be increased.

Examples of the unsubstituted C1-C20 alkyl group of Formula 1 include amethyl group, an ethyl group, a propyl group, an isobutyl group, asec-butyl, a pentyl group, an iso-amyl group, and a hexyl group. Atleast one of the hydrogen atoms in the C1-C20 alkyl group may besubstituted with a halogen atom, a C1-C30 alkyl group, a C1-C30 alkoxygroup, a lower alkylamino group, a hydroxy group, a nitro group, a cyanogroup, an amino group, an amidino group, hydrazine, hydrazone, acarboxyl group, a sulfonic acid group, a phosphoric acid group, or thelike.

The unsubstituted C6-C20 aryl group of Formula 1 refers to a carbocyclicaromatic system having one or more rings, which may be fused orconnected to each other using a pendent method. The term “aryl” includesaromatic radicals, such as a phenyl, a naphthyl, and atetrahydronaphthyl. In addition, at least one of the hydrogen atoms inthe C6-C20 aryl group may be substituted with substituents describedwith reference to the C1-C20 alkyl group.

The unsubstituted C2-C20 heteroaryl group of Formula 1 refers to amonovalent monocyclic radical that includes 1, 2, or 3 atoms selectedfrom N, O, P, and S and includes a ring composed of 2 to 30 carbonatoms. Examples of the C2-C20 heteroaryl group include a pyridyl, athienyl, and a furyl. At least one of the hydrogen atoms in the C2-C20heteroaryl group may be substituted with substituents described withreference to the C1-C20 alkyl group.

Hereinafter, a method of preparing a dye-sensitized gel electrolyte,according to aspects of the present invention, will be described.According to an exemplary embodiment of the present invention, a polymerhaving a hydrogen bonding group is mixed with a diacid, and the mixtureis reacted at a temperature between 40 and 45° C., to obtain anon-volatile polymer solvent that is hydrogen bonded to the diacid.

According to another exemplary embodiment of the present invention, twotypes of polymers, having different hydrogen bonding groups, are mixedare a predetermined molar ratio, and the mixture is reacted at atemperature between 40 and 45° C., to obtain a non-volatile polymersolvent, in which the polymers are hydrogen bonded to each other. Then,an iodized salt and iodine are added to the non-volatile polymersolvent, to complete the preparation of a dye-sensitized gelelectrolyte.

As described above, an organic solvent is not essential in the gelelectrolyte. This differs from typical gel electrolytes and liquidelectrolytes, which generally require an organic solvent.

When the non-volatile polymer solvent is mixed with the iodine and theiodized salt, a nano metal oxide mixture may further be added thereto.The nano metal oxide mixture includes the nano metal oxide dispersed ina volatile organic solvent. The mixture is stirred and pulverized, usingultrasonic waves.

The volatile organic solvent may be acetonitrile, methoxypropionitrile,or the like, and the amount of the volatile organic solvent may rangefrom 1000 to 10000 parts by weight, based on 100 parts by weight of thenano metal oxide. After the mixture is added to the non-volatile polymersolvent, the resultant is dried to remove the volatile solvent andcomplete the manufacture of a gel electrolyte including the nano metaloxide.

FIG. 1 is a cross-sectional view of a dye-sensitized solar cell,according to an exemplary embodiment of the present invention. Referringto FIG. 1, the dye-sensitized solar cell includes a first substrate 10,an opposing second substrate 20, and a gel electrolyte 30 disposedtherebetween. A first electrode 11, a porous layer 13, and a dye 15 aredisposed on the first substrate 10. A second electrode 21 is disposed onthe second substrate 20.

The first substrate 10, which supports the first electrode 11, istransparent. The first substrate 10 may be formed of a transparent glassor plastic, for example. Examples of the plastic include polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC),polypropylene (PP), polyimide (PI), and triacetyl cellulose (TAC).

The first electrode 11 may be formed of a transparent material selectedfrom the group consisting of an indium tin oxide, an indium oxide, a tinoxide, a zinc oxide, a sulfur oxide, a fluorine oxide, a mixturethereof, ZnO—Ga₂O₃, and ZnO—Al₂O₃. The first electrode 11 may include asingle, or multiple layers of the transparent material.

The porous layer 13 is formed on the first electrode 11. The porouslayer 13 includes metal oxide particles 131 having a minute andgenerally uniform average particle diameter. The metal oxide particles131 can be formed using a self-assembly method. The porous layer 13 mayalso have nanoporous properties, due to having a fine and uniform poresize. The average diameter of pores of the porous layer 13 may rangefrom 7.5 nm to 15 nm.

The thickness of the porous layer 13 may range from 10 nm to 3000 nm,and in particular from 10 nm to 1000 nm. However, the thickness of theporous layer 13 is not limited thereto. The dye 15, which absorbs lightand generates exited electrons, is adsorbed into the surface of theporous layer 13.

The metal oxide particles 131 may be formed of a titanium oxide, a zincoxide, a tin oxide, a strontium oxide, an indium oxide, an iridiumoxide, a lanthan oxide, a vanadium oxide, a molybdenum oxide, a tungstenoxide, a niobium oxide, a magnesium oxide, an aluminium oxide, a yttriumoxide, a scandium oxide, a samarium oxide, a gallium oxide, a strontiumtitanium oxide, or the like. In this regard, the metal oxide particles131 are formed of TiO₂, SnO₂, WO₃, ZnO, or a complex thereof, inparticular.

The dye 15 included in the porous layer 13 may be any substance that isused in solar cells or photocells. For example, the dye 15 may be aruthenium (Ru) complex. The Ru complex may be RuL₂(SCN)₂, RuL₂(H₂O)₂,RuL₃, or RuL₂ (L is 2,2′-bipyridyl-4,4′-dicarboxylate).

However, the dye 15 can be any dye that has a suitable charge separationcapability and is sensitized when exposed to light. For example, the dye15 can be, in addition to Ru complex, an xanthene type pigment, such asrhodamine B, rose gengal, eosine, or erythrosine; a cyanine-typepigment, such as quinocyanine or cryptocyanine; a basic dye, such asphenosafranine, Capri blue, thiocine, or methyleneblue; chlorophyl; aporphyrin-based compound, such as zinc porphyrin, or magnesiumporphyrin; other azo pigments; a complex compound, such as aphthalocyane compound or Ru trisbipyridiyl; antraquinone-based pigment;or polycyclic quinine-based pigment. These compounds can be used aloneor in combination.

The second substrate 20 supports the second electrode 21 and may betransparent. In this regard, the second substrate 20, like the firstsubstrate 10, may be formed of glass or plastic.

The second electrode 21 faces the first electrode 11 and may include atransparent electrode 21 a and a catalyst electrode 21 b. Thetransparent electrode 21 a may be formed of a transparent material, suchas an indium tin oxide, a fluoro tin oxide, an antimony tin oxide, azinc oxide, a tin oxide, ZnO—Ga₂O₃, ZnO—Al₂O₃, or the like. Thetransparent electrode 21 a may include a single, or multiple layers ofthe transparent material. The catalyst electrode 21 b activates a redoxcouple, and may be formed of Pt, Ru, Pd, Ir, Rh, Os, C, WO₃, TiO₂, orthe like.

The first substrate 10 is attached to the second substrate 20, using anadhesive 41. A gel electrolyte forming composition is injected betweenthe first electrode 11 and the second electrode 21, through a hole 25 adefined in the second substrate 20 and the second electrode 21. The gelelectrolyte forming composition is then used to form the gel electrolyte30.

The gel electrolyte 30 transfers electrons from the second electrode 21to the dye 15, through oxidation and reduction. The hole 25 a is sealedusing an adhesive 42 and a glass cover 43.

The gel electrolyte forming composition is prepared by mixing a polymerhaving a hydrogen bonding group, a diacid, a solvent that can dissolvethe polymer or the diacid, an iodized salt, and iodine. In thealternative, the gel electrolyte forming composition may be prepared bymixing two types of polymers having hydrogen bonding groups, a solventthat can dissolve the polymers, an iodized salt, and iodine. The gelelectrolyte forming composition is injected into the dye-sensitizedsolar cell, at a temperature at which hydrogen bonds are not formedbetween the polymer and the diacid, or between the two types ofpolymers. The temperature ranges from 80 to 120° C.

Although not shown in FIG. 1, the gel electrolyte 30 may also beprepared according to the following process. The gel electrolyte formingcomposition 30 may be directly coated on the porous layer 13 and dried,to form the gel electrolyte 30. This coating process is conducted atconditions and temperatures at which hydrogen bonds are formed betweenthe polymer and the diacid, or between the two types of polymers.

Next, the adhesive 41 is disposed on the first substrate 10, aroundwhere the gel electrolyte 30 is formed. The resulting structure iscovered with the second substrate 20. The adhesive 41 may be athermoplastic polymer film, for example Suryln (DuPont Chemical Co.).The resultant structure is hot-pressed, to obtain a dye-sensitized solarcell.

Aspects of the present invention will now be described in greaterdetail, with reference to the following examples. The following examplesare for illustrative purposes only and are not intended to limit thescope of the invention.

Example 1 Preparation of a 2-H (Two Hydrogen Bonding Sites) HydrogenBonding Electrolyte

1 g of 1 M poly(ethylene glycol) dimesylate (Mw: 2,000 g/mol) (n is 33in Formula 5) and 0.138 g of calcium carbonate were mixed, and themixture was dissolved in 31.44 g of acetonitrile. Then, 2 Mpyrimethamine was added thereto, and the mixture was reacted at 70° C.,for 48 hours, while stirring, to obtain a compound represented byFormula 4 (a=33). The weight average molecular weight of the compound ofFormula 4 was 2295.42 g/mol.

1 g of the compound of Formula 4 was filtered, using a mixed solution of30 ml of THF and 30 ml of penthane, to obtain an intermediate. Theintermediate and 0.07 g of 1M glutaric acid were dissolved in 30 ml ofacetone, and the resultant mixture was reacted at 70° C., for 72 hours,to obtain a 2-H, hydrogen bonding, non-volatile, polymer solvent.

The 2-H, hydrogen bonding, non-volatile, polymer solvent was mixed with1-methyl-3-propylimidazolium iodide (MPII), at a molar ratio of 20:1,and 10 parts by weight of I₂, based on 100 parts by weight of MPII, wasadded thereto, to complete the preparation of a gel electrolyte. All ofthe reagents in Example 1 were purchased from Aldrich Chemical Co.

Example 2 Preparation of 3-H (Three Hydrogen Bonding Sites) HydrogenBonding Gel Electrolyte

1 M poly(ethylene glycol)-(succinimidyl succinate)₂ (Mw=2,000 g/mol) (nis 33 in Formula 7) and 2 M cytosine were dissolved in a solution of 20ml of acetonitrile and 20 ml of dichloromethane, and the mixture wasreacted at 40° C., for 24 hours, while stirring, to obtain a compound ofFormula 2 (b=33). The weight average molecular weight of the compound ofFormula 2 was 2,100 g/mol.

1M poly(ethylene glycol)-(succinimidyl succinate)₂ (Mw=2,000 g/mol) and2M guanine were dissolved in a solution of 20 ml of acetonitrile and 20ml of dichloromethane, and the mixture was reacted at 40° C., for 24hours, while stirring, to obtain a compound of Formula 3 (c=33). Theweight average molecular weight of the compound of Formula 3 was 2,132g/mol.

1 mole of the compound of Formula 2 and 1 mole of the compound ofFormula 3 were dissolved in 30 ml of acetonitrile, and the mixture wasreacted at 30° C., for 72 hours, to obtain a 3-H, hydrogen bonding,non-volatile, polymer solvent.

The obtained 3-H, hydrogen bonding, non-volatile, polymer solvent wasmixed with 1-methyl-3-propylimidazolium iodide (MPII), at a molar ratioof 20:1. 10 parts by weight of I₂, based on 100 parts by weight of MPII,was added thereto, to complete the preparation of an ionic gelelectrolyte. All of the reagents in Example 2 were purchased fromAldrich Chemical Co.

Example 3 Preparation of 2-H Hydrogen Bonding Electrolyte IncludingSilica Nano Particles

10 parts by weight of fumed silica nano particles, having an averageparticle diameter of 20 nm, was added to 100 parts by weight of the 2-H,hydrogen bonding, gel electrolyte prepared according to Example 1, toprepare a 2-H, hydrogen bonding, gel electrolyte including silica nanoparticles. In order to disperse the nano particles, 20 parts by weightof acetonitrile, as a volatile organic solvent, based on 100 parts byweight of the electrolyte, was added thereto, and the mixture wasstirred and sonicated. The dispersed nano particles were dried in anoven at 50° C., for 24 hours, and then further dried in a vacuum for 24hours to remove the acetonitrile solvent, thereby completing thepreparation of a gel electrolyte.

Example 4 Preparation of 2-H Hydrogen Bonding Electrolyte Including TiO₂Nano Particles

10 parts by weight of rutile TiO₂ nano particles (Tayca, Japan), havingan average particle diameter of 100 nm, was added to 100 parts by weightof the 2-H, hydrogen bonding, gel electrolyte prepared according toExample 1, to prepare a 2-H, hydrogen bonding, gel electrolyte includingTiO₂ nano particles.

In order to disperse the nano particles, 20 parts by weight ofacetonitrile, based on 100 parts by weight of the electrolyte, was addedthereto, and the mixture was stirred and sonicated. The dispersed nanoparticles were dried in an oven at 50° C., for 24 hours, and furtherdried in a vacuum for 24 hours, to remove the acetonitrile solvent,thereby completing the preparation of a gel electrolyte.

Comparative Example 1 Preparation of Liquid Electrolyte

Poly(ethylene glycol) (Mw: 2,000 g/mol) was mixed with1-methyl-3-propylimidazolium iodide (MPII), at a molar ratio of 20:1. 10parts by weight of iodine, based on 100 parts by weight of MPII, wasadded thereto, to complete the preparation of a liquid electrolyte.

The ion conductivity of each of the electrolytes of Examples 1-4 andComparative Example 1 was measured at 30° C., and the results are shownin Table 1 below.

TABLE 1 Ion conductivity Electrolyte (S/cm) 2-H electrolyte (Example 1)5.00 × 10⁻⁴ 3-H electrolyte (Example 2) 3.81 × 10⁻⁴ 2-H/silicaelectrolyte (Example 3) 6.12 × 10⁻⁴ 2-H/TiO₂ electrolyte (Example 4)7.45 × 10⁻⁴ Non-hydrogen bonding electrolyte 1.06 × 10⁻⁴ (ComparativeExample 1)

As shown in Table 1, the electrolytes prepared according to Examples 1-4had improved ion conductivities, as compared to the electrolyte preparedaccording to Comparative Example 1. The ion conductivities wereincreased in the electrolytes of Examples 1-4, since the moleculestherein were arranged, due to the binding of the solvent molecules. Theion mobility was improved, even though the gelation was achieved byhydrogen bonds. In addition, the 2-H electrolyte, which has relativelyweak hydrogen bonds, had a higher ion conductivity than the 3-Helectrolyte. This phenomenon can be explained by a difference inflexibility between the molecular chains in the solvents, due to thehydrogen bonds. When nano metal oxide particles were added to theelectrolyte, as in Examples 3 and 4, the gelation properties of theelectrolytes were improved, due to the binding force among the nanometal oxide particles. In addition, the nano metal oxide particlespromoted ion mobility, since the ions were adsorbed on the surface ofthe nano metal oxide particles.

Ion conductivities, of the electrolyte prepared according to Example 1,were measured according to temperature, and the results are shown inTable 2 below.

TABLE 2 Temperature (° C.) Ion conductivity (S/cm) 20 4.00 × 10⁻⁴ 305.00 × 10⁻⁴ 45 1.74 × 10⁻³ 60 3.64 × 10⁻³

According to Table 2, the ion conductivity of the electrolyte wasincreased, as the temperature was increased. In particular, the ionconductivity was greater than 10⁻³S/cm at a temperature of at least 45°C. The ion conductivity was improved, as compared to the ionconductivity of a conventional gel electrolyte, which is less than 10⁻⁴S/cm.

FIG. 2 is a graph illustrating viscoelastic (gelation) properties of thegel electrolyte (2-H electrolyte) prepared according to Example 1, whichwere measured by a dynamic mechanical analysis (DMA). According to FIG.2, it can be confirmed that the gel electrolyte was not converted to aliquid state, even at temperatures of 50° C., or higher, due to thehydrogen bonds. Typical solar cells operate a temperature of 60° C., orless, so the gel electrolyte according to Example 1 had stable gelationproperties.

Comparative Example 2 Preparation of Dye-Sensitized Solar Cell

A dispersion of titanium oxide particles, having a particle diameter ofabout 10 nm, was coated on 1 cm² of a first conductive film formed ofITO, using a doctor blade, and the resultant was calcined at 450° C.,for 30 minutes, to prepare a porous layer having a thickness of 10 μm.

Then, the resultant was heated at 80° C. and immersed in 0.3 mM of a dyedispersion including a Ru(dcbpy)2(NCS)2(dcbpy=2,2′-bipyridyl-4,4′-dicarboxylato) (535-bisTBA, Solaronix,Swiss)) dye, that was dissolved in ethanol. This dye absorptiontreatment was performed for longer than 12 hours.

The porous layer having the absorbed dye was washed with ethanol anddried at room temperature, to prepare a first electrode including alight absorbing layer. A second electrode was prepared by depositing asecond conductive film formed of Pt on the first conductive film formedof ITO, using a sputter. A hole having a diameter of 0.75 mm was formedin the second electrode using a drill, in order to inject anelectrolyte.

A support, formed of a thermoplastic polymer film having a thickness of60 μm, was placed between the first and second electrodes. The first andsecond electrodes were pressed together at 100° C., for 9 seconds, toprepare an assembly. Then, the liquid electrolyte of Comparative Example1 was injected into the assembly, through the hole in the secondelectrode. The hole was then sealed using a cover glass and athermoplastic polymer film, to complete the preparation of adye-sensitized solar cell. 1-hexyl-2,3-dimethyl imidazolium iodide, 0.1M lithium iodide, 0.05 M iodine, and 0.5 M 4-tert-butylpyridine weredissolved in 3-methoxypropionitrile, to prepare the electrolyte.

Example 5 Preparation of Dye-Sensitized Solar Cell

A dispersion of titanium oxide particles, having a particle diameter ofabout 10 nm, was coated on 1 cm² of a first conductive film formed ofITO, using a doctor blade. The resultant structure was calcined at 450°C., for 30 minutes, to prepare a porous layer having a thickness of 10μm.

The resultant structure was maintained at 80° C. and immersed in 0.3 mMof a dye dispersion of a Ru(dcbpy)₂(NCS)₂(dcbpy=2,2′-bipyridyl-4,4′-dicarboxylato) (535-bisTBA, Solaronix,Swiss)) dye that was dissolved in ethanol. This dye absorption treatmentwas performed for longer than 12 hours.

The resultant porous layer having the absorbed dye was washed withethanol and dried at room temperature, to prepare a first electrodeincluding a light absorbing layer. A second electrode was prepared bydepositing a second conductive film formed of Pt on the first conductivefilm formed of ITO, using a sputter.

The composition of Example 1 was coated on the first electrode and driedto prepare a gel electrolyte. The composition was prepared by mixing0.94 g of the compound of Formula 4, 0.06 g of glutaric acid, and 11.45ml of acetonitrile as a solvent, to form a non-volatile solvent. Thenon-volatile solvent was mixed with 1-methyl-3-propylimidazolium iodide(MPH), at a molar ratio of 20:1. 10 parts by weight of I₂, based on 100parts by weight of MPH, were then added thereto.

A support, formed of a thermoplastic polymer film having a thickness of60 μm, was placed between the first and second electrodes. The first andsecond electrodes were pressed together at 100° C., for 9 seconds,thereby completing the preparation of a dye-sensitized solar cell.

Example 6

A dye-sensitized solar cell was prepared in the same manner as inExample 5, except that the composition of Example 2 was used instead ofthe composition of Example 1. The composition was prepared by mixing0.49 g of the compound of Formula 2, 0.51 g of the compound of Formula3, and 11.45 ml of acetonitrile as a solvent, to form a non-volatilesolvent. The non-volatile solvent was mixed with1-methyl-3-propylimidazolium iodide (MPH), at a molar ratio of 20:1. 10parts by weight of I₂, based on 100 parts by weight of MPH, where thenadded thereto.

Example 7

A dye-sensitized solar cell was prepared in the same manner as inExample 5, except that the composition of Example 3 was used instead ofthe composition of Example 1.

The composition of Example 3 was prepared in the same manner as inExample 2, except that fumed silica nano particles, having an averageparticle diameter of 20 nm, were further added to the composition ofExample 2.

Example 8

A dye-sensitized solar cell was prepared in the same manner as inExample 5, except that the composition of Example 4 was used instead ofthe composition of Example 1. The composition of Example 4 was preparedin the same manner as in Example 2, except that 0.09 g of rutile TiO₂nano particles (Tayca, Japan), having an average particle diameter of100 nm, was further added to the composition of Example 2.

Photoelectric conversion characteristics of the dye-sensitized solarcells, prepared according to Examples 5-8 and Comparative Example 2,were measured at 100 mW/cm², and the results are shown in Table 3 below.

TABLE 3 Open Photoelectric circuit Short circuit conversion voltagecurrent Fill factor efficiency Voc (V) Jsc (mA · cm⁻²) FF (%) η (%)Example 5 0.71 10.4 62 4.63 Example 6 0.69 10.1 65 4.53 Example 7 0.7210.0 72 5.36 Example 8 0.71 14.1 65 6.39 Comparative 0.71 7.3 66 3.84Example 2

As shown in Table 3, the photoelectric conversion efficiencies, of eachof the dye-sensitized solar cells of Examples 5-8, were higher than thatof the dye-sensitized solar cell of Comparative Example 2. In addition,the photoelectric conversion efficiency of the dye-sensitized solar cellof Example 8 (including the TiO₂ nano particles) was higher than thedye-sensitized solar cell of Example 7 (including silica nanoparticles). Since the TiO₂ nano particles have a physically weakerbinding force than the silica nano particles, the TiO₂ nano particleshad better ion conductivity and light scattering effects in theelectrolyte layer. That is, the photoelectric conversion efficiency wasimproved, since light that was not absorbed in the photocathode layerwas scattered by the particles included in the electrolyte and thenabsorbed.

FIG. 3 is a graph illustrating optical current characteristics,according to the optical voltage of a dye-sensitized solar cell preparedaccording to Example 8. Referring to FIG. 3, the dye-sensitized solarcell of Example 8 had excellent photoelectric conversioncharacteristics.

Although a few exemplary embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these exemplary embodiments, withoutdeparting from the principles and spirit of the invention, the scope ofwhich is defined in the claims and their equivalents.

1. A dye sensitized solar cell comprising: opposing first and secondelectrodes; a porous disposed between the first electrode and secondelectrode, comprising an adsorbed dye; a gel electrolyte disposedbetween the first electrode and the second electrode, comprising anon-volatile polymer solvent, the non-volatile polymer solventcomprising a first polymer having a hydrogen bonding group with at leasttwo hydrogen bonding sites.
 2. The dye sensitized solar cell of claim 1,wherein the gel electrolyte further comprises at least one metal oxideselected from the group consisting of TiO2, WO3, ZnO, Nb2O5, SnO2, SiO2and TiSrO3.
 3. The dye sensitized solar cell of claim 1, wherein the gelelectrolyte further comprises iodine and an iodised salt.
 4. The dyesensitized solar cell of claim 1, wherein the non-volatile polymersolvent further comprises a second polymer that is hydrogen bonded tothe first polymer.
 5. The dye sensitized solar cell of claim 1, whereinthe gel electrolyte further comprises a diacid that is hydrogen boned tothe first polymer.
 6. The dye sensitized solar cell of claim 5, whereinthe diacid comprises at least one selected from the group consisting ofglutaric acid, malonic acid, and adipic acid.
 7. The dye sensitizedsolar cell of claim 1, wherein the gel electrolyte further comprises anup-conversion phosphor and/or a down-conversion phosphor.
 8. The dyesensitized solar cell of claim 1, wherein the dye comprises RuL₂(SCN)₂,RuL₂(H₂O)₂, RuL₃, or RuL₂ (L is 2,2′-bipyridyl-4,4′-dicarboxylate). 9.The dye sensitized solar cell of claim 1, wherein the first polymer is apolyalkylene oxide-based compound having a weight average molecularweight of 2000 g/mol, or less.
 10. The dye sensitized solar cell ofclaim 1, wherein the first polymer comprises at least one compoundselected from the group consisting of compounds represented by Formulae1 to 3 below:

wherein R1 is selected from the group consisting of a substituted orunsubstituted C1-C20 alkyl group, a substituted or unsubstituted C6-C20aryl group, and a substituted or unsubstituted C2-C20 heteroaryl group,R2 is selected from the group consisting of a substituted orunsubstituted C1-C20 alkyl group, a substituted or unsubstituted C6-C20aryl group, and a substituted or unsubstituted C2-C20 heteroaryl group,and a is an integer from 1 to 50;

wherein b is an integer from 1 to 50; and

wherein c is an integer from 1 to
 50. 11. The dye sensitized solar cellof claim 10, wherein the compound of Formula 1 is represented by Formula4:

wherein a is an integer from 1 to
 33. 12. The dye sensitized solar cellof claim 4, wherein the first polymer comprises a compound representedby Formula 2 below, and the second polymer comprises a compoundrepresented by Formula 3 below:

wherein b is an integer from 1 to 50; and

wherein c is an integer from 1 to 50.